Partial combustion or gasification of coal involves reacting the coal at elevated temperatures and possibly elevated pressures with a limited volume of oxygen, the reaction preferably being carried out in the presence of additional agents such as steam, carbon dioxide, or various other materials. Gasification of coal produces a gas, known as synthesis gas, that contains mostly carbon monoxide and hydrogen. Also produced are varying quantities of other gases, such as carbon dioxide and methane, and various liquid and solid materials, such as small particles of ash and carbon commonly known and collectively defined herein as flyslag or flyash. This flyslag, because it is derived from a "reducing" atmosphere, tends to be different in composition and properties from flyash normally associated with combustion boilers where a fully oxidizing atmosphere is utilized. For example, the flyslag from processes for partial combustion of coal may contain elemental iron, sulfides, and deposited carbon, components not normally associated with boiler flyash. In general, the flyslag or flyash entrained with the gas in partial combustion processes is usually removed from the raw synthesis gas by a combination of cyclones or separators, or a water scrubbing system employing washer coolers, venturi scrubbers, or filters or electrostatic precipitators, or combinations of these systems.
The raw synthesis gas from the gasifier or gasification zone contains, in addition to the aforementioned materials, sulfur-containing gases, such as hydrogen sulfide and carbonyl sulfide, as well as small amounts of ammonia and hydrogen cyanide. The presence of HCN, NH.sub.3, and COS in synthesis gas derived from the gasification of coal complicates removal of additional impurities such as H.sub.2 Sand/or CO.sub.2, and poses problems insofar as product quality and pollution control requirements are concerned. Although HCN, NH.sub.3, and COS are present, as indicated, in quite minor quantities, for example, normally less than 1 percent by volume, combined, of the total raw synthesis gas stream, they must be dealt with before the synthesis gas is utilized.
The flyslag or flyash removed from the synthesis gas may have undesirable properties insofar as its ultimate disposal is concerned. For example, it may be light, friable, dusty and difficult to compact. Because it may contain unsuitable species such as arsenic, selenium, and sulfides, it must be handled with care, and, if it is to be utilized or disposed of as land fill, must be in a form which does not release such materials readily to the environment. The sulfides present are particularly troublesome since, upon contact with strongly acidic material, hydrogen sulfide will be evolved. The invention addresses the problems of flyslag treatment, concomitantly accomplishing the treatment and utilization of other nominal waste products from the gasification process.